1. Field of the Invention
The present invention relates to a memory module for a computer and to a socket into which the memory module is inserted.
2. Description of the Related Arts
A computer that performs a highly complicated tasks such as manipulating a high resolution graphics typically requires a large memory capacity and a wide data bus. Thus, a memory module for the computer must include many contact terminals, through which a microprocessor communicates with the memory module. In addition, the memory module typically requires several contact terminals for power signals since high microprocessor speed makes the memory module susceptible to signal noise. The large number of the contact terminals makes the memory module large and prevents miniaturization of the computer.
A conventional memory module has multiple memory devices (or ICs) mounted on a printed wiring board (PWB), and the PWB has multiple contact terminals for power signals, control signals, address signals, or data signals from a mother board of a computer system. Typical memory module types include a SIMM (single in-line memory module) and a DIMM (dual in-line memory module). In both types, contact terminals are arranged along a bottom edge of the PWB on a front and back surfaces of the PWB. In the SIMM type, two opposite contact terminals that face each other across the PWB are for the same signal, but in the DIMM type, the two opposite contact terminals are designated for different signals.
FIGS. 1 and 4 respectively show a typical memory module and the module when inserted in a socket. The memory module has multiple semiconductor memory devices 3 mounted on a PWB 1, and contact terminals 5 are along a bottom edge of PWB 1. A socket 7, in which the memory module is inserted, is installed on a mother board of a computer. Socket 7 has contact terminals (not shown) for contacting respective contact terminals 5 of the memory module. The memory module communicates via socket 7 with a microprocessor and other control devices which may be mounted on the mother board. That is, power signals (Vcc, Vdd, Vss), control signals, address signals and data signals. are transferred between the memory module and the microprocessor and other devices via the contact terminals of socket 7.
In designing wiring patterns of the memory module, a short signal path from an external terminal of a semiconductor device to a corresponding contact terminal of the memory module is desirable. However, physical restrictions on the PWB make some signal paths 4a and 4b (FIG. 1) undesirably long. Moreover, when external terminals from different semiconductor devices mounted on different locations of the PWB connect to a common contact terminal of the memory module, the signal paths from the common contact terminal to respective semiconductor devices may differ. The long and uneven signal paths can cause signal noise, a signal delay and a clock skew that may result in a malfunctioning of the computer. Therefore, a way to design the signal paths of the memory module as short and even to one another as possible is needed.
In accordance with an embodiment of the present invention, a memory module includes contact terminals formed along at least one transverse (or side) edge as well as a longitudinal (or bottom) edge of the memory module. The addition of the contact terminals along transverse edges can promote an efficient wiring of a printed wiring board (PWB) for the memory module. The transverse contact terminals on the side of the memory module can be designated for any signals. For example, power lines (for Vcc or Vdd), ground lines (for GND or Vss), address lines, control lines through which memory module control signals pass, and any other lines can connect to the transverse contact terminals.
Another embodiment of the present invention provides a socket for the above-described memory module. The socket includes a horizontal portion, into which the bottom edge of the memory module inserts, and a vertical portion, into which a vertical edge of the memory module inserts. All contact terminals of the memory module contact respective contact terminals formed in the horizontal and vertical portions of the socket. The vertical portion can be made of a flexible circuit carrier or a connector head that rotatably attaches to the horizontal portion.